What you need

What to do

Adult supervision is recommended.
Carefully fill the jar with several inches of water. Add a slightly smaller
amount of oil to the jar. Which settles on top? Add several drops of food
colouring. What happens?

Sprinkle salt onto the surface of the
liquid as you count slowly to five. Cool! Keep adding salt to continue to
effects.

What is happening

Oil and water have different
densities. This means that one is heavier than the other is. Since the water in
on the bottom and the oil is on the top, water is the more dense liquid. Oil and
water do not mix because they have different chemical properties that act to
repel each other rather than to attract. When you add salt to the surface, it
combines with the oil layer to make the oil heavier. This causes the oil to sink
into the water layer. Salt is very soluble in water, which means that is easily
dissolves out of the oil into the water. When this happens, the oil becomes
lighter again and returns to the surface of the water. This can happen over and
over again until the water becomes saturated with salt and it no longer able to
dissolve the salt. But salt is very soluble in water and it takes a lot of salt
to completely saturate water. So you are guaranteed lots of fun!